One method of operating internal combustion engines consists of supplying gaseous fuel into a combustion chamber, adding air to get a particular air to fuel ratio (AFR), and then igniting the mixture, typically with a spark from a sparkplug in a conventional manner known to those skilled in the art. If this ignition is done with a relatively low AFR, then the resulting combustion tends to occur very quickly, and at a very high temperature. This can result in the formation of nitrogen-oxygen compounds (NOx).
One method of reducing the formation of NOx is thus to use a higher AFR or otherwise lean mixture, which results in a slower burn at a lower temperature. However, spark ignition becomes more difficult as the amount of fuel per unit volume decreases. Additionally, small scale turbulence in the spark gap makes the formation of suitable ignition sparks difficult. The increasing use of recirculated exhaust gas to affect the relative “richness” or “leanness” of the overall mixture has created additional challenges to igniting mixtures in the cylinders as desired.
Several methods have been developed in response to the difficulties encountered in attempting to run gaseous engines via lean burn strategies, such as an AFR on the order of 68:1. One method is to use a prechamber and sparkplug. A typical prechamber and sparkplug configuration includes at least one orifice leading to the combustion chamber. A spark gap is positioned inside the prechamber, and attached to an electrical lead. Because of the small size and relative isolation of the prechamber, turbulence in the fuel and air mixture therein is significantly reduced, facilitating the formation of sparks and flame generation. A spark arcs across the spark gap and ignites a combustion reaction inside the prechamber. The prechamber combustion propagates and expels a jet(s) of burning gas through the orifice(s) into the combustion chamber of the engine, which serves to ignite the main fuel charge in the combustion chamber. More recent designs will have more than one orifice so the flame will propagate on multiple fronts simultaneously, resulting in more efficient ignition. The art teaches different models for such sparkplugs such as U.S. Pat. Nos. 5,947,076 and 4,987,868. There are also examples of designs which attempt to increase the efficiency of the prechamber such as U.S. Pat. No. 5,105,780.
At specific conditions the internal combustion initiation device is optimally efficient, but as the AFR varies with engine operating condition, the efficiency of the engine may be reduced. This can result in the fuel burning too quickly, which results in increased temperature and increased NOx output, or the fuel incompletely burning which results in unburned hydrocarbons in the exhaust. While the most advanced of these prechamber sparkplugs enable a broader range of AFR's for a given engine than formerly available designs, there remains room for improvement.
The present disclosure is directed to one or more of the problems or shortcomings set forth above.